AQUATIC INSECTS 889 



Dragonflies and Damselflies {Order Odonata) 



This is another isolated group of insects, larger in size and of 

 stronger build. All our representatives of the group are aquatic 

 in their earlier stages, but there are a few Hawaiian damselflies 

 whose nymphs live out of the water, on moist soil under the leaves 

 of Hliaceous plants. All members of the order are carnivorous in 

 all stages. They are indeed among the most important of carni- 

 vorous forms about the shores of all fresh waters. 



The wings of the adults are strongly developed and have a 

 peculiar venation (Fig. 1388). The legs are not used for walking, 

 but only for perching; to facilitate perching on vertical stems, 

 they are set far forward and graduated in length, so that they hold 

 the body when at rest in a more or less horizontal position. This 

 facilitates quick stopping and starting again. Correspondingly 

 the wings are shifted far backward, and tilted upward at their 

 fore margins, and the side pieces of the thorax are askew. 



The males are peculiar also among the orders in having the 

 accessory organs of reproduction (copulatory apparatus) developed 

 upon the ventral side of the second abdominal segment, far re- 

 moved from the opening of the sperm ducts upon the ninth segment. 

 The eyes are very highly developed, and the antennae are minute 

 and setaceous. In this they resembl the preceding order Ephem- 

 erida, but the two groups as they exist to-day are highly differenti- 

 ated from each other, although more or less intermediate fossil 

 forms point to their common origin in the past. 



Among the dragonflies are many superb flyers. The speed on 

 the wing of Tramea and Anax equals, and their agility exceeds, 

 that of swallows. They all capture their prey in flight, and are 

 dependent on their wings for getting a living. But the habit of 

 flight is very different in different groups. Only a few of the 

 strongest forms roam the upper air at will. There is a host of 

 beautiful species, the skimmers or Libellulidae (Fig. 1360), that 

 hovers over ponds in horizontal flight, the larger species on tireless 

 wings, keeping to the higher levels. The stronger fljang Aeschnidae 

 course along streams on more or less regular beats: but the Gom- 

 phines are less constantly on the wing, flying usually in short 



